I am not sure where to start with this one. But here it goes...
We implemented a new email server this weekend. We can send and recieve, everything appears to be in working order. However, we have a web application that sends email updates using SMTP. It can send to external email accounts (e.g. gmail,comcast)fine. But it does not send to exchange, email@example.com
Diagnostic-Code: smtp;550 5.1.1 User unknown
Not sure what is going on. Need some help.
The application pulls emails from the application DB. It worked fine last week with our old email server. The email accounts are the same. No migration of account. Started fresh.